In an effort to reduce dependence on foreign oil as well as the associated economic and environmental costs of importation and distribution, many countries are now producing alcohol fuel, i.e. methanol and ethanol, from coal and domestically-grown crops, respectively. Gasoline blends of such fuels are also presently available to the consumer for automotive and related vehicle and industrial uses.
In Brazil, for example, compositions of ethanol/gasoline fuels are available in blends of 22% and 95% ethanol in gasoline, designated as E22 and E95. Ethanol and methanol blended fuels are the predominant alternative fuels used in so-called "flex" cars today, i.e. cars which run on "flexible" or alternative fuels. Ethanol and methanol blended fuels have been widely accepted because they are environmentally friendly alternatives to petroleum-based fuels since they improve exhaust emissions and are a readily renewable resource.
Vehicles calibrated to specific alcohol blended fuel compositions have been developed for production and have been found to function well provided that the intended fuel blend is used. However, as understood by those skilled in the art, if varying blends of alcohol/gasoline are provided, the vehicles do not operate at stoichiometry and thus do not provide the proper ratio of air and fuel which is required for combustion to provide maximum fuel efficiency, maximum power and minimal emissions.
In an effort to overcome this calibration problem, automotive manufacturers have typically utilized flexible fuel sensors which are discrete components operative to directly measure the alcohol concentration of fuel introduced into the engine. This information is read by the engine control computer and the correct air/fuel ratio for different fuels is adjusted on a real-time basis and maintained. While these so-called "flexible fuel systems" have been designed and implemented in North American vehicles, the systems have been found to be prohibitively expensive to implement on a wide scale commercial basis because of the significant cost of the flexible fuel sensor.
Vehicle designers have thus turned attention toward the development of "sensorless" flexible fuel systems. See, for example, the publications 1992 Geneva Motor Show Proceedings "Saab ECO Sport", pp. 33-34, and Flexible Fuel System Without Fuel Sensor, which reference Autorotor SW Patent 8903129-8. The Saab ECO Sport referenced in the Geneva Motor Show publication embodies the disclosure of the Autorotor patent. The system requires an active fuel pump and utilizes complex engine control strategy to calculate the correct fueling with the system. In operation, the additional fuel pump allows for only the stored fuel from the previous drive to be used for start-ups. Thus, additional information is provided regarding "same fuel" during the entire open-loop time period. See also, the publication "Development of a BMW Flexible Fuel Vehicle", by Werner Muhl and Heinrick Petra. This publication discloses a system which uses a fuel composition sensor and which indicates that the incorporation of an adaptive lambda control is not feasible.
Consequently, a need has developed for a "sensorless" flexible fuel system and, in particular, a flexible alcohol system which does not utilize any active additional components and will accommodate a wide range of alcohol and gasoline fuel concentrations from 0 to 100 percent alcohol (A0-A100) while still maintaining acceptable emission and performance objectives.